This invention relates to pressure vessels having at least one open end and to end closures and side ports therefor. More specifically, it relates to cylindrical pressure vessels designed for reverse osmosis pressure driven filtration operations, particularly to vessels which provide full-bore access to accept elongated, cylindrical filtration media cartridges. Even more particularly, it relates to improved end closure arrangements for such pressure vessels. It also relates to methods for making such pressure vessels of this general type and particularly to those designed for pressure driven filtration operations, especially filtration using filter cartridges, and more particularly to making vessels suited for sidewall porting to provide fluid flow couplings through the cylindrical sidewall of the pressure vessel.
Cylindrical pressure vessels have many industrial applications, including use in the field of filtration. Vessels used in filtration are often of the type made from a resin-coated fiberglass shell and having a fully open end that must be closed by a separate closure. Further, one or more side ports are often attached to a cylindrical side wall of such a vessel.
There are a variety of approaches used in the industry to anchor these side ports into vessels with fully open ends. They include threading into the body wall, counterboring a relief from the inside into which a flange of the port can reside, forming a concentric relief during the winding which will serve to pocket the port flange, and overmolding sealing material onto the vessel.
It is desirable to seal the port flange against the inside wall of the pressure vessel. The inside wall is rich in resin and provides a good seal. However, since the wall cylindrical, a special ring or other sealing means is necessary to provide an adequate seal, thus adding to the overall cost of production.
Counterboring creates a flat surface allowing standard o-rings or other less-expensive sealing means to be used. However, counterboring cuts into structural glass fibers which weakens the vessel.
Providing a concentric relief can require a difficult to produce side port flange design, also adding to the overall cost of production.
Further, regarding high pressure vessels, it is common in the industry to imbed a metallic ring in the composite shell of a full-bore opening vessel to provide a place to anchor the end closure. An example is shown in U.S. Pat. No. 5,720,411, wherein a metallic annular element is fixedly imbedded in a shell. Low-pressure units can be fabricated without such an insert ring.
As the burst test pressure requirements elevate considerably, in those configurations with the end closure seal adjacent to the insert ring, the exact configuration of the insert ring becomes crucial. That is, for 8″ diameter vessels that must only survive test pressures up to 3600 psig there are a variety of configurations that function satisfactorily. These same insert rings have been shown to be inadequately retained as test pressures approach 6000 psig, in vessels of the same inside diameter.